The present invention relates to an improved trimmer head for use in flexible line rotary trimming devices used to trim grass, weeds and other vegetation. More particularly, the invention is directed to an improvement in the line loading of both “bump-feed” type trimmer heads such as those disclosed in U.S. Pat. Nos. 4,458,419, 4,959,904 and 6,901,667 and the more simple manually operated heads such as that disclosed in U.S. Pat. No. 7,275,324, issued Oct. 2, 2007. With minor modifications to accommodate the differences in the configurations of spool and housing, the improvement of the present invention could also be embodied in automatic heads of the type such as that disclosed in U.S. Pat. No. 5,063,673.
Trimmer heads used in flexible line rotary trimmers generally carry one or two lengths of flexible nylon cutting line wrapped about an interior spool with the ends of the line or lines projecting outwardly through opposed apertures in the side wall of the trimmer head. The head is threadably mounted on the end of an elongated shaft and rotated at a high velocity by a gas or electric motor so that the ends of the cutting line project radially from the head and sever weeds or other vegetation. When cutting line projecting from the head breaks off or becomes overly worn, it must be severed and fresh line extended from the spool through the line outlet eyelets in the side of the housing. Bump-feed type heads include a line feed-out mechanism which responds to a bump on the ground intentionally applied by the operator to feed out a measured length of fresh cutting line which is typically cut to the desired length by a knife blade projecting from a shield attached to the trimmer above the cutting head and spaced a predetermined distance from the perimeter of the trimmer head housing. Manual heads do not include any such line feed-out mechanism. The spool must be manually rotated relative to the housing to pay out additional cutting line. Automatic heads include a mechanism that detects a loss of mass in the cutting line projecting from the head during use and, without the need for any action by the operator, pay out additional lengths of line from the spool through the eyelets.
In each of these types of heads, the length or lengths of cutting line are typically wound onto the spool by hand. As most cutting heads employ a single length of line wrapped about a spool with the end portions projecting from opposed sides of the cutting head, care must be taken during the winding of the spool to avoid crossing or otherwise tangling the line within the spool which interferes with the paying out of fresh line. This is particularly important in automatic and bump-feed heads where centrifugal force is utilized to pull the new lengths of line from the spool during use as the head is being bumped against the ground as any line tangle will interfere with the proper feeding of the line. Difficulty in properly loading the line on the spool is the most common complaint of home users of flexible line trimmers. It also is a time consuming task for the professional user.
An example of a bump-feed head is found in U.S. Pat. No. 4,458,419, the contents of which are incorporated herein by reference as though fully set forth below. As described therein in detail, the trimmer head contains a spool holding one or more coils of cutting line and a simplified mechanism that selectively allows relative movement of the spool with respect to the housing in response to bumping of the head on the ground to pay out measured lengths of line. The simplified pay-out mechanism includes a spring-loaded cam and cam follower arrangement in which the cam follower includes two pairs of diametrically opposed and generally inwardly facing abutment surfaces arrayed about the axis of rotation of the trimmer housing. The abutment surfaces are spaced 90° apart and are carried by a depending cylindrical wall that circumscribes an interior chamber. The cam member is disposed within the chamber in threaded engagement with the extended lower end of the drive bolt of the trimmer housing and defines two vertically adjacent cams, each cam being of a square configuration and defining four perpendicularly disposed cam surfaces adapted to engage the abutment surfaces on the cam follower. The upper cam was rotationally offset 45° from the lower cam.
In operation, the housing is rotationally driven by the drive bolt through a connection between the upper end of the bolt and the trimmer drive means. The cam member is attached to the housing and thus is also driven by the drive bolt. The cam member in turn drives the cam follower and the spool that is mounted thereon due to the operative engagement between the cam surfaces on the cam member and the abutment surfaces on the cam follower. The line carrying spool is disposed about the cylindrical wall of the cam follower and is attached thereto via a pair of opposed outwardly projecting studs on the cam follower member that extend into slots formed in the inner portion of the spool. The spool is provided with a bumper at its lower end such that when the bumper is pressed against or bumped on the ground, the housing moves downwardly with respect to the spool against the force of a spring, disengaging the lower cam from the abutment surfaces on the cam follower and allowing the cam member to rotate 45° relative to the cam follower, whereupon the cam surfaces of the upper cam abut the abutment surfaces on the cam follower. That imparts a similar degree of relative rotation between the spool and the housing. Once the force of the bump is dissipated, the spring loading forces the spool and housing back to their relative positions, which releases the cam surfaces on the upper cam from the cam follower abutment surfaces and allows another 45° of relative rotation of the cam member and cam follower and thus of the spool and housing, for a total of 90° of rotation per bump, which provides the predetermined relative rotation between the housing and spool needed to pay out a desired length of line through the apertures in the trimmer housing. Other examples of bump-feed type trimmer heads are found in U.S. Pat. Nos. 4,959,904 and 6,901,667, the contents of which are also incorporated herein by reference as though fully set forth below.
In many of these trimmer heads, it is necessary to separate the spool from the housing to wind the cutting line about the spool. Various channel configurations in and through the spool have been developed that enable the line to be fed onto the spool through the eyelets in the housing without having to first remove the spool from the housing. Examples of such heads are found in U.S. Pat. Nos. 5,765,287 and 6,263,580 and in Applicant's U.S. Pat. No. 7,275,324, filed Oct. 2, 2007 which is incorporated herein by reference as though fully set forth herein. While these configurations do facilitate the loading of line onto the spool, they do not eliminate the need to remove the spool from the housing (known in the trade as splitting the head) in the event the cutting line breaks proximate the eyelet during use. Unfortunately, this is a frequent occurrence when the rapidly rotating line strikes a solid object such as a fence post. When such breakage occurs, the load pulling outwardly on the line during use is effectively eliminated and the line recoils, drawing the severed end of the line inwardly through the housing eyelet. Fresh line can no longer be paid out through the eyelets without first splitting the head to gain access to the spool in order to unwind fresh line from the spool and thread the fresh line through the eyelet in the housing. The trimmer heads of the present invention enable the user to quickly and easily uniformly wind lengths of cutting line onto the spool and to remove and reload line on the spool without having to split the head even in those instances where line breakage occurs proximate the housing eyelet during use.